The modern communications era has brought about a tremendous expansion of wireline and wireless networks. Computer networks, television networks, and telephony networks are experiencing an unprecedented technological expansion, fueled by consumer demand. Wireless and mobile networking technologies have addressed related consumer demands, while providing more flexibility and immediacy of information transfer.
Current and future networking technologies continue to facilitate ease of information transfer and convenience to users. One such delivery technique that has shown promise is Digital Video Broadcasting (DVB). In this regard, DVB-T, which is related to DVB-C (cable) and DVB-S (satellite), is the terrestrial variant of the DVB standard. As is well known, DVB-T is a wireless point-to-multipoint data delivery mechanism developed for digital TV broadcasting, and is based on the MPEG-2 transport stream for the transmission of video and synchronized audio. DVB-T has the capability of efficiently transmitting large amounts of data over a broadcast channel to a high number of users at a lower cost, when compared to data transmission through mobile telecommunication networks using, e.g., 3G systems. Advantageously, DVB-T has also proven to be exceptionally robust in that it provides increased performance in geographic conditions that would normally affect other types of transmissions, such as the rapid changes of reception conditions, and hilly and mountainous terrain. On the other hand, DVB-H (handheld), which is also related to DVB-T, can provide increased performance particularly for wireless data delivery to handheld devices.
Digital broadband data broadcast networks are known. As mentioned, an example of such a network enjoying popularity in Europe and elsewhere world-wide is DVB which, in addition to the delivery of television content, is capable of delivering data, such as Internet Protocol (IP) data. Other examples of broadband data broadcast networks include Japanese Terrestrial Integrated Service Digital Broadcasting (ISDB-T), Digital Audio Broadcasting (DAB), and MBMS, and those networks provided by the Advanced Television Systems Committee (ATSC). In many such systems, a containerization technique is utilized in which content for transmission is placed into MPEG-2 packets which act as data containers. Thus, the containers can be utilized to transport any suitably digitized data including, but not limited to High Definition TV, multiple channel Standard definition TV (PAUNTSC or SECAM) and, of course, broadband multimedia data and interactive services.
As will be appreciated by those skilled in the art, digital broadband data broadcast networks can be implemented in a distributed transmission system, often referred to as a single frequency network. In such a network, a content source provides digital broadband data to a plurality of co-channel transmitters, all of which synchronously transmit the same content. More particularly, all of the transmitters in a single frequency network must generally transmit the same signals on the same frequency, and at the same time. The precision of synchronization depends on the scheme used to modulate the broadcast content. The accuracy of synchronization, however, can be in the nanosecond range (the more accurate the synchronization between the transmitters, the better the receiving conditions).
To enable the transmitters in a single frequency network to all transmit the same signals on the same frequency, the content source can provide the transmitters with a common transport stream, such as by means of a multiplexer or an IP encapsulator in the case of an IP datacast (IPDC) DVB-T/H network. Then, the common transport stream can be sent to the transport stream to the transmitters across a distribution network, and from the transmitters to a plurality of terminals. But for all of the transmitters to transmit the transport stream at the same time, the transport stream can include markers that permit the transmitters to synchronize the transport stream in time. The markers can define a reference between a position in the bit stream and a time reference. In this regard, to properly synchronize the transport stream, the transmitters typically have a common, and typically high-resolution, time reference.
Techniques have been developed to synchronize the transmitters of a single frequency network. In the case of DVB-T/H, for example, a technique to synchronize transmitters sending DVB-T/H content across a single frequency network is disclosed by the European Telecommunications Standards Institute (ETSI) Technical Specification (TS) 101 191, entitled: Digital Video Broadcasting (DVB): DVB Mega-Frame for Single Frequency Network (SFN) Synchronization v. 1.4.1 (2004) and related specifications, the contents of which are hereby incorporated by reference in its entirety. In accordance with the technique disclosed by ETSI TS 101 191, the single frequency network includes a transport stream source, sometimes referred to as a “head-end,” that is located at a point in the single frequency network where the common transport stream is available, and can be implemented as part of a multiplexer, IP encapsulator or another separate entity. This head-end can facilitate synchronization of the transmitters by sending the transmitters timing information calculated based on a repetitive time reference and a frequency reference from a source, such as a global positioning system (GPS), which can provide a one pulse-per-second (pps) time reference and 10 MHz frequency reference, the time reference being provided with a resolution of 100 ns. The transmitters can then be synchronized with 100 ns accuracy based on the timing information and the same time and frequency references.
Since the head-end and transmitters of the technique of ETSI TS 101 191 utilize a source such as GPS to synchronize the transmitters, the head-end and transmitters typically require a GPS antenna to receive the time reference and frequency reference. Since many transmission sites having a transmitter also have mast, also placing a GPS antenna with a view to all directions at such sites is typically not an issue. However, since the head-end may comprise a server or other computer system located in an isolated space (e.g., server room), placing a GPS antenna with a view to all directions at the head-end location may undesirably complicate configuring of the single frequency network. Thus, it would be desirable to design a system and method of synchronizing a single frequency network transmission stream in a manner that achieves the same accurate synchronization as the ETSI TS 101 191 technique, without requiring a high-resolution time source (e.g., GPS source) at the head-end.